Chemical additives are used throughout the petroleum industry for increasing the rate or total amount of hydrocarbon compounds recovered from subterranean hydrocarbon-bearing reservoirs. Conventionally, chemical additives including one or more surfactants (and optionally other materials such as polymers) are combined with a fluid, usually a water source, and this combination is injected underground. Such combinations may be referred to as “injectates.” The injected surfactants lower the interfacial tension between the fluid and/or connate (subterranean water source) and the hydrocarbon (oil); and may further change the wettability of the reservoir rock, thereby increasing the yield of hydrocarbon compounds released and/or the rate of their recovery.
Injectates are suitably optimized for use in one or more specific industrial processes directed to maximizing yield of hydrocarbon recovery from a subterranean reservoir, maximizing the rate of recovery of hydrocarbon from a subterranean reservoir, or both. Such use may be before or after establishment of a well, wherein “well” is understood to indicate a fluid connection between a hydrocarbon within a subterranean reservoir, and a point proximal to the surface of the earth suitably situated to allow collection of the hydrocarbon from the reservoir. In man-made wells, this point may be referred to as a wellbore, which is a man-made fluid connection to a subterranean hydrocarbon-bearing reservoir. The wellbore may be adapted to collect hydrocarbon, to inject one more injectates, or both by including one or more pipes, tanks, pumps and the like. The use of injectates is not generally limited by the type of reservoir or the type of hydrocarbon, and injectates are injected into nearly every such formation in order to maximize yield of hydrocarbon obtained from the reservoir.
For example, injectates may be injected contemporaneously with establishment of a well, such as by hydraulic fracturing. An injectate may suitably be combined with a proppant, wherein the combination is a fracturing fluid. The fracturing fluid is used in a hydraulic fracturing process to establish a well. Surfactants present in the fracturing fluid may achieve well stimulation during fracturing, wherein applied hydraulic pressure can further assist in distributing the surfactants within the reservoir. Hydraulic fracturing techniques are useful to form new wells as well as to extend the life of existing wells. Injectates including surfactants are known to be useful in both of these applications.
Injectates are also used in enhanced recovery of hydrocarbons from wells. “Enhanced hydrocarbon recovery” refers to processes carried out after a well is established for the purpose of increasing the rate or total amount of hydrocarbon collected. Enhanced hydrocarbon recovery is typically initiated once a reduction in the rate of collection of hydrocarbon from the well is observed, in order to “reinvigorate” the well (often referred to in the art as secondary oil recovery) and/or when collection has substantially stopped (often referred to in the art as tertiary oil recovery). Injectates for enhanced hydrocarbon recovery conventionally include surfactants and/or polymers.
However, surfactants employed in injectates and fracturing fluids may adsorb substantially onto the rock surfaces after injection, depleting the surfactant quickly at the expense of deeper-lying rock surfaces. Additionally, many injected surfactants facilitate underground emulsion formation between the hydrocarbon and connate, which retards or prevents recovery of the hydrocarbon. Even further, surfactants and mixtures thereof are often unstable or insoluble in the high temperature and/or high total dissolved solids water sources encountered in some subterranean reservoirs. For example, in some reservoirs temperatures in excess of 60° C. are encountered; temperatures can be as high as 250° C. Additionally, underground water (connate) is often characterized as having high total dissolved solids, such as about 4 wt % total dissolved solids and as much as about 35 wt % total dissolved solids. In some cases, a substantial portion of the dissolved solids are ionic (one or more salts).
Even further still, surfactants and mixtures thereof are often unstable or insoluble in concentrations above about 1-10 wt % active ingredients (non-solvent chemical additives). In some instances this instability is due to electronic interactions between ionic surfactants employed in the mixtures. Thus, conventional surfactant mixtures, such as concentrates for use in forming injectates, requires the incorporation, transportation, and storage of mixtures having as much as 90 wt % inactive ingredients. Such use of inactive ingredients is inefficient and wasteful.
In addition to the foregoing problems known to exist in the injectate art, there is a paucity of injectate compositions that are effective to increase either the rate or amount of hydrocarbon recoverable from wells characterized as having “tight” or “very tight” subterranean reservoir rock. Such tight rock is characterized as having permeability of about 0.1 milliDarcy (mD) or less, with “very tight” rock characterized as having permeability of about 0.01 mD or less. Some hydrocarbon-bearing shale formations have permeability as low as 0.0001 mD for example. Efficient recovery of hydrocarbons trapped within a tight rock matrix is a known problem in the industry. As petroleum supplies from conventional oilfield rock become depleted, technologies addressing the problem of tight rock will increase in importance and value.
There is also a paucity of solutions for improving rate or amount of hydrocarbon recovered from reservoirs where the crude hydrocarbon is characterized as “heavy oil”, that is, hydrocarbon having American Petroleum Institute gravity or “API gravity” of about 28 or less as “crude” hydrocarbon recovered from the well. API gravity is a measure of how dense a petroleum liquid is compared to water, wherein the density of water is 10. API gravity of greater than 10 correlates to a petroleum liquid that has lower density than water, whereas API gravity of less than 10 correlates to a petroleum liquid that has higher density than water. Generally, though not always, heavier oils have lower paraffin content and higher content of asphaltenes, resins (polymerized materials), and aromatic compounds than lighter oils. Efficient recovery of heavy oil is a known problem in the industry.
There is a need in the industry for compositions that reduce the interfacial tension between a fluid and hydrocarbon trapped within subterranean rock formations without adsorbing strongly to the rock surfaces. There is a need in the industry for compositions that are stable in high temperature environments, high total dissolved solids environments, or high temperature/high total dissolved solids environments. There is a need in the industry for compositions that increase the yield of hydrocarbon compounds recovered from subterranean reservoirs without forming subterranean water-oil emulsions. There is a need in the industry for concentrated compositions (concentrated injectates) to improve efficiency of manufacturing and transportation thereof. There is a need in the industry for concentrated compositions that are easily and quickly diluted prior to or during injection thereof into subterranean environments that include high total dissolved solids, high temperature, or a combination thereof. There is a need in the industry for compositions that increase the yield of hydrocarbon compounds recovered during hydraulic fracturing operations. There is a need in the industry for compositions that increase the yield of hydrocarbon compounds recovered during enhanced hydrocarbon recovery operations. There is a need in the industry for compositions that increase the yield of hydrocarbon compounds recovered from tight rock or very tight rock formations. There is a need in the industry for compositions that increase the yield of hydrocarbon recovered from reservoirs wherein the crude hydrocarbon has an API gravity of about 28 or less.